Slate roofs are appreciated for their aesthetic and durable qualities. However, they are expensive and the weight of the slate is quite high compared to composition shingles; and, as a result, they are typically two to four times more expensive as composition asphalt roofing. Thus, utility lies in any application of slate on a roof which will reduce the amount of slate needed to effectively cover a roof. Applicants' method and slate roof herein provide for such utility.
A good background for slate roofing and the method for installing the same may be found in the NRCA Roofing and Waterproofing Manual--4th Edition, pp. 1179-1227, that document being incorporated herein by reference. Typical slate roofs are constructed in the manner set forth in FIG. 1, labeled "prior art". With reference to FIG. 1, it is seen that a wood roof is first covered with an underlayment layer, typically asphalt felt paper, to which overlapping slate courses are applied with slate covering the roof in two plies except where there is overlap, in which case there are three plies of slate. Through joints should not occur from the slate roof surface to the felt.
Applicant, however, has removed a slate layer and replaced it with heavy-duty, weatherproof interlayment material layer, typically plastic 20 to 60 mil in thickness.